[acveilleux]

There's a few things at play here.

Economy of scales is huge of course. A lot of the parts are actually shared between many different cars at different price points. There can be on the order of 50+ micro-controller in that car. Do you want to pay 10$ extra for each of them just because they have cooler specs?

The various parts are designed at various times so that car might have controllers for the anti-lock braking system that were designed 5 years ago.

Hard real-time applications (brakes, ECU, etc.) don't magically need more gigahertz, that engine with direct injection only needs to calculate fuel volume maybe 20000 times per seconds (once per cylinder per 2 rpm) and that would probably be a ridiculous upper bound.

In-car navigation and entertainment packages are completely separate from the hardware actually controlling the car.